Forse cosi

codice:
function getPerleRob() 
{ 
   $query = "select perla from tb_rob"; 
   $result = mysql_query($query,$this->db_conn) or die (mysql_error()); 
   while ($queryGetPerleRob[] = mysql_fetch_array($result)) {}; 
   return $queryGetPerleRob; 
}